1,186 research outputs found
Temperature and light requirements for growth of two diatom species (Bacillariophyceae) isolated from an Arctic macroalga
In the present study, two abundant epiphyticdiatom taxa were isolated from the assimilation hairs ofthe brown macroalga Chordaria flagelliformis collected inthe Arctic Kongsfjorden (Spitsbergen, Norway), establishedas unialgal cultures and their growth rates determinedunder controlled photon fluence rate andtemperature conditions. Using morphological (light andscanning electron microscopy) and SSU rRNA gene databoth isolates (ROS D99 and ROS D125) were identifiedas members of a FragilariaSynedropsis clade. Themolecular data of ROS D99 and ROS D125 were notidentical to any other published sequence. While ROSD99 has been identified as Fragilaria barbararum mainlydue to the SEM characteristics, ROS D125 could not bedefinitely identified although morphological data speakfor Fragilaria striatula. Both diatom species showedsimilar growth rates at all temperatures and photon fluencerates tested. They grew well between 0 and 15Cwithoptimum temperatures of 1214C, but did not survive20C. Therefore, compared to Antarctic diatoms bothtaxa from Kongsfjorden can be characterised as eurythermalorganisms. Increasing photon fluence rates between2 and 15 lmol m2 s1 were accompanied with analmost twofold increase in growth rates, but photon fluencerates >15 lmol m2 s1 did not further enhancegrowth pointing to low light requirements. From thesedata optimum, minimum and maximum photon fluencerates and temperatures for growth can be assessed indicatingthat both diatoms are well acclimated to the fluctuatingenvironmental conditions in the Arctic habitat
Numerical modelling of methyl iodide in the eastern tropical Atlantic
Methyl iodide (CH3I) is a volatile organic halogen compound that contributes significantly to the transport of iodine from the ocean to the atmosphere, where it plays an important role in tropospheric chemistry. CH3I is naturally produced and occurs in the global ocean. The processes involved in the formation of CH3I, however, are not fully understood. In fact, there is an ongoing debate whether production by phytoplankton or photochemical degradation of organic matter is the main source term. Here, both the biological and photochemical production mechanisms are considered in a biogeochemical module that is coupled to a one-dimensional water column model for the eastern tropical Atlantic. The model is able to reproduce observed subsurface maxima of CH3I concentrations. But, the dominating source process cannot be clearly identified as subsurface maxima can occur due to both direct biological and photochemical production. However, good agreement between the observed and simulated difference between surface and subsurface methyl iodide concentrations is achieved only when direct biological production is taken into account. Production rates for the biological CH3I source that were derived from published laboratory studies are shown to be inappropriate for explaining CH3I concentrations in the eastern tropical Atlantic
Lattice sum rules for the colour fields
We analyse the sum rules describing the action and energy in the colour
fields around glueballs, torelons and static potentials.Comment: 9 pages LATEX, (typos corrected, to appear in Phys Rev D
The chiral and flavour projection of Dirac-Kahler fermions in the geometric discretization
It is shown that an exact chiral symmetry can be described for Dirac-Kahler
fermions using the two complexes of the geometric discretization. This
principle is extended to describe exact flavour projection and it is shown that
this necessitates the introduction of a new operator and two new structures of
complex. To describe simultaneous chiral and flavour projection, eight
complexes are needed in all and it is shown that projection leaves a single
flavour of chiral field on each.Comment: v2: 17 pages, Latex. 5 images eps. Added references, reformatted and
clarification of some point
Cold atoms in non-Abelian gauge potentials: From the Hofstadter "moth" to lattice gauge theory
We demonstrate how to create artificial external non-Abelian gauge potentials
acting on cold atoms in optical lattices. The method employs internal
states of atoms and laser assisted state sensitive tunneling. Thus, dynamics
are communicated by unitary -matrices. By experimental control of
the tunneling parameters, the system can be made truly non-Abelian. We show
that single particle dynamics in the case of intense U(2) vector potentials
lead to a generalized Hofstadter butterfly spectrum which shows a complex
``moth''-like structure. We discuss the possibility to employ non-Abelian
interferometry (Aharonov-Bohm effect) and address methods to realize matter
dynamics in specific classes of lattice gauge fields.Comment: 5 pages, 3 figure
Quantitative profiling of hydroxy lipid metabolites in mouse organs reveals distinct lipidomic profiles and modifications due to elevated n-3 fatty acid levels
Polyunsaturated fatty acids (PUFA) are precursors of bioactive metabolites and mediators. In this study, the profile of hydroxyeicosatetraenoic (HETE), hydroxyeicosapentaenoic (HEPE) and hydroxydocosahexaenoic (HDHA) acids derived from arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in colon, liver, lung, spleen, muscle, heart and kidney tissue of healthy wildtype mice were characterized, and compared to profiles in organs from transgenic fat-1 mice engineered to express the Caenorhabditis elegans fat-1 gene encoding an n-3 desaturase and thereby with endogenously elevated n-3 PUFA levels. PUFAs were measured using gas chromatography. The lipid metabolites were assayed using LC-MS/MS. AA and DHA were the prominent PUFAs in wildtype and fat-1 mice. EPA levels were low in both groups even though there was a significant increase in fat-1 organs with an up to 12-fold increase in fat-1 spleen and kidney. DHA levels increased by approximately 1.5-fold in fat-1 as compared to wildtype mice. While HETEs remained the same or decreased moderately and HDHAs increased 1- to 3-fold, HEPE formation in fat-1 tissues increased from 8- (muscle) to 44-fold (spleen). These findings indicate distinct profiles of monohydroxy lipid metabolites in different organs and strong utilization of EPA for HEPE formation, by which moderate EPA supplementation might trigger formation of biologically active EPA-derived resolvins
Recursive Construction of Generator for Lagrangian Gauge Symmetries
We obtain, for a subclass of structure functions characterizing a first class
Hamiltonian system, recursive relations from which the general form of the
local symmetry transformations can be constructed in terms of the independent
gauge parameters. We apply this to a non-trivial Hamiltonian system involving
two primary constraints, as well as two secondary constraints of the Nambu-Goto
type.Comment: 10 pages, Late
Measure of the path integral in lattice gauge theory
We show how to construct the measure of the path integral in lattice gauge
theory. This measure contains a factor beyond the standard Haar measure. Such
factor becomes relevant for the calculation of a single transition amplitude
(in contrast to the calculation of ratios of amplitudes). Single amplitudes are
required for computation of the partition function and the free energy. For
U(1) lattice gauge theory, we present a numerical simulation of the transition
amplitude comparing the path integral with the evolution in terms of the
Hamiltonian, showing good agreement.Comment: 5 pages, 2 figure
A new look at the modified Coulomb potential in a strong magnetic field
The static Coulomb potential of Quantum Electrodynamics (QED) is calculated
in the presence of a strong magnetic field in the lowest Landau level (LLL)
approximation using two different methods. First, the vacuum expectation value
of the corresponding Wilson loop is calculated perturbatively in two different
regimes of dynamical mass , {\it i.e.}, and , where
is the longitudinal components of the momentum relative to
the external magnetic field . The result is then compared with the static
potential arising from Born approximation. Both results coincide. Although the
arising potentials show different behavior in the aforementioned regimes, a
novel dependence on the angle between the particle-antiparticle's axis
and the direction of the magnetic field is observed. In the regime
, for strong enough magnetic
field and depending on the angle , a qualitative change occurs in the
Coulomb-like potential; Whereas for the potential is repulsive,
it exhibits a minimum for angles .Comment: V1: 26 pages, 8 figures, latex format, V2: Accepted for publication
in PRD (2007
Improved lattice operators for non-relativistic fermions
In this work I apply a recently proposed improvement procedure, originally
conceived to reduce finite lattice spacing effects in transfer matrices for
dilute Fermi systems, to tuning operators for the calculation of observables. I
construct, in particular, highly improved representations for the energy and
the contact, as a first step in an improvement program for finite-temperature
calculations. I illustrate the effects of improvement on those quantities with
a ground-state lattice calculation at unitarity.Comment: 11 pages, 7 figures; replaced with published versio
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